1. Field of the Invention
The present invention relates to a back-up device for an IP-PBX (Internet Protocol-Private Branch Exchange) targeting a failure of an IP-PBX, an IP-PBX back-up system and a failure coping method of a system.
2. Description of the Related Art
Conventional back-up device for IP-PBX is in general equipped with a back-up device for the purpose of coping with physically different networks. Such a conventional IP-PBX system as shown in FIG. 7, for example, includes physically different networks 41 and 42, a network 40 connecting the networks, an IP-PBX device (hereinafter referred to as a private branch exchange or a private branch exchange 100) and IP terminals 10 and 11 connected to the network 41, and IP terminals 12 and 13 connected to the network 42 (see e.g. Japanese Patent Laying-Open (Kokai) No. Showa 63-285053 which will be referred to as Literature 1 hereinafter).
Thus structured conventional IP-PBX system operates in the following manner.
The IP terminals 12 and 13 connected to the network 42 transmit a terminal operation start request to the private branch exchange 100 through the network 40, and the private branch exchange 100 searches stored terminal data for a terminal whose registration is requested and when such a terminal exists in the data, puts the relevant IP terminal under the control of the private branch exchange 100, whereby thereafter a transmission request from the IP terminal and an arrival instruction from other IP terminal are all transmitted to the IP terminals through the networks 40 and 42 according to the private branch exchange 100.
In other words, the IP-PBX device itself and the IP terminal are connected by a network communicable by using a TCP/IP (Transport Control Protocol/Internet Protocol) such as a LAN (Local Area Network) or the Internet. This enables an IP terminal disposed at a place physically and geographically apart to be controlled only by a central IP-PBX (private branch exchange) without disposing an IP-PBX at the site in question.
In the above-described Literature 1, a network management interface for the switching between a main unit and a spare unit exists within a communication network. Switching between the main unit and the spare unit is conducted by the network management interface.
On the other hand, in Japanese Patent Laying-Open (Kokai) No. Heisei 7-154429 (hereinafter referred to as Literature 2), when a first IP (Internet Protocol) router develops a failure, a second IP router takes over a MAC (Media Access Control) address and an IP address of an IP router at an address indicated by a node of the first IP router. According to the technique, with a LAN-WAN-LAN (Local Area Network-Wide Area Network-Local Area Network) connected IP router duplexed, a secondary IP router monitors a state of a primary IP router and when the primary IP router develops a failure, the secondary IP router takes over information and an address of the primary IP router to realize automatic duplexing of the IP routers and compensate for communication between terminals.
The above-described conventional art have the following shortcomings.
The first problem is that a failure occurring in a network such as a LAN or the Internet makes control of an IP terminal completely impossible to prevent continuation of normal operation of the IP terminal. In particular, crucial is that not only a physical cable failure but also a software failure of a router might be a cause of impossible control.
The reason is that in a case where a control signal for controlling an IP terminal is transmitted as a packet by a TCP/IP protocol and a communication path of the packet develops a failure, when the packet fails to reach an IP-PBX or the IP terminal, the control signal for controlling the terminal arrives neither. As a result, control of the IP terminal is disabled.
In particular, when using a network to which unspecified numbers of apparatuses and networks are connected such as the Internet, reliability of each network can not be secured for sure. Therefore, a possibility that normal operation will continue will be reduced.
In the above-described Literature 2, at the time of a failure, the back-up device takes over an IP address and a MAC address of the main device and completely replaces the main device to operate. Therefore, when a communication path to the device is cut off, there will remain no detouring method.